Advanced wood pellet

ABSTRACT

The present invention relates generally to an advanced wood pellet used for producing energy where under combustion, the advanced wood pellet produces vapors that have less acid, burns hotter, and thereby burns more completely resulting in less ash during combustion when compared to traditional wood pellets.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of U.S. provisional patent application No. 61/718,397, entitled “Method of Producing a Wood Pellet” filed on Oct. 25, 2012 and U.S. provisional patent application No. 61/718,350, entitled “The Production of an Advanced Wood Pellet” filed on Oct. 25, 2012, the contents of the aforementioned applications are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates generally to an advanced wood pellet used for producing energy where under combustion, the advanced wood pellet produces vapors that have less acid, burns hotter, and thereby burns more completely resulting in less ash during combustion when compared to traditional wood pellets.

BACKGROUND

Typically, wood pellets that are produced for fuel comprise of wood material which is first processed to produce a uniform dough-like mass. This dough-like mass is then fed through a pellet mill or pellet press which includes a die having holes of a size configured to produce the pellet. The high pressure of pressing the dough-like mass through the pellet press causes the temperature of the wood to increase greatly and to naturally adhere.

It has been known in the industry that wood pellets for fuel are a good source of energy due to the low energy required to produce and transport the wood pellets. Also, due to the diminishing quantities, qualities and hazards of securing natural resources such as coal, petroleum, and natural gas products, wood pellets have become an even more important renewable resource for fuel.

Unfortunately, some of the byproducts produced when using wood pellets as a fuel is still undesirable. Such byproducts may include, but are not limited to, unwanted solids such as ash and undesirable vapors containing various forms of acid, dioxides and other chemicals that are harmful to the environment.

Furthermore, it is the common understanding that wood pellet production often requires addition of a binding agent because the binding properties of the wood lignins naturally found in the wood biomass are insufficient for maintaining the shape and structure of wood pellets. U.S. Pat. No. 4,236,897, WO 2009/139621, and WO 2009/044375 all utilize additional materials to form wood pellets, including, for example, thermoplastic materials, flours, oxidizing compounds, zeolites, adsorbents, starches, and the like. The methods of producing a wood pellet as disclosed in these publications discuss the difficulties of achieving a wood pellet without binding agents. In addition the temperature at which the wood pellets are produced in conventional wood pellet mills typically occurs at a temperature ranging from 212° F. to about 350° F., where wood lignins melt at less than 392° F. (Beis, et al. (2010) “Fast Pyrolysis of Lignins,” BioResources 5(3): 1408-1424). Considering this, the lignins are often not in the form or structure to adequately act as a binder for conventional wood pellets.

The removal of unwanted particulates in the wood material prior to forming a wood pellet is another known common factor understood in the manufacturing process of the wood pellet that directly relates to the quality of the wood pellets. More specifically, if the manufacturing process does not include the removal of unwanted particulates such as rocks, additional minerals and metal, such unwanted particulates will be present in the wood pellet thereby causing a more impure and lower quality or inferior wood pellet. Therefore, there is a need for a wood pellet that produces fewer undesirable by products that are less acidic, that burns hotter, and more completely during combustion.

SUMMARY

The deficiencies of the prior art are substantially overcome in consideration of the invention disclosed herein. More specifically, additional innovation and advantages are realized when smartly manufacturing a wood pellet to produce an advanced wood pellet which comprises additional substances to obtain a preferred result during combustion when used as an energy source.

One object of the invention relates to providing an advanced wood pellet that yields a cleaner and more completely combusted energy source over a traditional wood pellet, where the advanced wood pellet has been treated such that the advanced wood pellet consists of calcium carbonate and wood.

Another object of the invention is directed at providing an advanced wood pellet that yields a cleaner and more completely combusted energy source over a traditional wood pellet, where the advanced wood pellet has been treated such that the advanced wood pellet comprises of calcium carbonate, wood and calcium salt.

Yet another object of the invention relates to providing an advanced wood pellet that yields a cleaner and more completely combusted energy source over a traditional wood pellet, where the advanced wood pellet has been treated such that the advanced wood pellet comprises of calcium carbonate, wood and other inert material. Non-limiting examples of inert materials that may be found in calcium carbonate tailings, for example, include vegetable oil, animal fat, chlorite, plagioclase, feldspar, quartz, mica, barium, toluene, petroleum products, tall oil, ortho-phenyl phenol, acetone, isopropyl alcohol, stearic acid, polyacrylamide, acrylamide monomer, polyacrylates, phosphorus, methyl isothiocyanate, ethylamine, and free chlorine.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the acetic acid exhaust gas graphical analysis after combusting a conventional wood pellet.

FIG. 2 shows the acetic acid exhaust gas graphical analysis after combusting an advanced wood pellet.

FIG. 3 illustrates a flow diagram for producing wood pellets according to an exemplary embodiment of the present invention.

FIG. 4 illustrates a flow diagram for producing advanced wood pellet according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

The following detailed description is of the best currently contemplated modes of carrying out exemplary embodiments of the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.

Various inventive features are described below that can each be used independently of one another or in combination with other features.

Embodiments of the present invention generally provide an advanced wood pellet which comprises calcium carbonate (CaCO₃), whereby the process for producing the advanced wood pellet results in a substantial amount of the calcium carbonate, for example, about 70 percent to about 90 percent of the total weight/amount of wood material, preferably about 80 percent, to have reacted with the wood material. Accordingly, this reaction neutralizes a majority of the acid within the wood material resulting in the wood material having a neutral pH which ranges from about 6 to about 8 with the preferred pH being 7. One embodiment of the chemical reaction that occurs to neutralize the various forms of acid is further illustrated in TABLE 1 below.

TABLE 1 Addition of Add Substance Reaction Results Acetic acid - Calcium Carbonate - H₂O, CO₂, and Calcium Ethanoate or 2C₂H₄O₂ CaCO₃ Calcium Acetate - Ca(CH₃COO)₂ [+residual CaCO₃ and acid]

Although some benefits are realized during the production of an advanced wood pellet whereby the process for producing an advanced wood pellet has been chosen such that a substantial amount of calcium carbonate reacts with the wood material. However, not all of the benefits are realized nor do they occur solely during the process for producing an advanced wood pellet.

Although an advanced wood pellet that comprises a more neutral pH when compared to a traditional wood pellet is an embodiment of the present invention, a more preferred embodiment of the present invention provides for an advanced wood pellet which substantially consists of a neutral pH and pure calcium carbonate. A preferred ratio of pure calcium carbonate to wood in an advanced wood pellet ranges from about 0.01 weight percent to about 0.1 weight percent. When an advanced wood pellet is used for energy, the combustion of the advanced wood pellet enables a further reaction between the acids in the wood material and the calcium carbonate thereby neutralizing any remaining acid and reducing other environmental contaminates such as methane gas, nitrogen oxides, and carbon monoxide.

In addition to the reduction of undesirable gases or vapors, the preferred advanced wood pellet containing calcium carbonate, where the pellet essentially has a neutral pH, produces a higher output temperature. Specifically, the level of BTUs may increase by as much as about 11% to about 13% when compared to a conventional wood pellet, thus yielding a cleaner and more completely combusted energy, resulting in less ash by volume, and extracting more energy from the advanced wood pellet when compared to a traditional wood pellet. Essentially the advanced wood pellet as provided here burns at a higher or hotter temperature resulting in a more complete combustion, which results in less solid byproduct, or ash, as well as fewer undesirable gases or vapors. The chemical reactions that occur when the wood biomass fuel is burned are identified in TABLE 2 below.

TABLE 2 CHEMICAL REACTION: Acid + Calcium Carbonate = Water + Carbon Dioxide + Calcium Salt CALCIUM SALT [+residual Acid and Calcium Carbonate] PRODUCED 2CH₂O₂ + CaCO₃ = H₂O + CO₂ + Ca(CHO₂)₂ Calcium methanoate 2C₂H₄O₂ + CaCO₃ = H₂O + CO₂ + Ca(C₂H₃O₂)₂ Calcium ethanoate 2C₃H₆O₂ + CaCO₃ = H₂O + CO₂ + Ca(C₃H₅O₂)₂ Calcium propanoate 2C₄H₈O₂ + CaCO₃ = H₂O + CO₂ + Ca(C₄H₇O₂)₂ Calcium butanoate 2C₆H₆O + CaCO₃ = H₂O + CO₂ + Ca(C₆H₅O₂)₂ Calcium phenoate 2C₇H₆O₂ + CaCO₃ = H₂O + CO₂ + Ca(C₇H₅O₂)₂ Calcium benzoate

A comparison of the results of high performance liquid chromatography (HPLC) analysis of acetic acid levels in the exhaust gas of a conventional wood pellet and the acetic acid levels in the exhaust gas of the inventive advanced wood pellet when they are burned was performed. The time taken for a particular compound to travel through the column of the HPLC device to the detector is known as its retention time. This time is measured from the time at which the sample is injected into the HPLC device to the point at which the display shows a maximum peak height for that compound. Different compounds have different retention times. When the conventional wood pellet exhaust gas sample was analyzed (FIG. 1), acetic acid was found to produce a peak labeled at 5.789 minutes and a retention time of 3.983 minutes (i.e., from the time of sample injection to detection). However, there was no peak when the acetic acid level was analyzed from the exhaust gas or burning of the inventive advanced wood pellet. Specifically, the 5.789 minutes acetic acid peak (or peak having a retention time of 3.983 minutes) was absent, indicating that there was no acetic acid found in the exhaust gas resulting from burning the advanced wood pellet as fuel (FIG. 2).

Burning 1 kg of wood may typically produce approximately 1.8 to 2.4 g of acetic acid. The chemical make-up of the acetic acid is 2CH₃COOH. However, when the acetic acid reacts with calcium carbonate at elevated temperatures during the combustion of the advanced wood pellet, the reaction creates water (H₂O), carbon dioxide (CO₂), and calcium acetate or calcium ethanoate [Ca(C₂H₃O₂)₂]. This chemical reaction basically neutralizes or eliminates the largest occurring acid. i.e., acetic acid, in the byproducts, smoke and ash.

The exhaust gases produced by combusting a conventional wood pellet and an advanced wood pellet were analyzed by HPLC. In the sample, pellets were burned for the purpose of producing energy and the exhaust gases or smoke was collected for HPLC analysis.

FIG. 1 shows the results of samples that were analyzed for acetic acid. Chromatography was used to separate the elements found in the byproducts when the wood was burned, specifically analyzing the levels of acetic acid. The samples were analyzed using a Multiplier of 1, a Dilution factor of 1, an injection volume of 75 microliters (μl), and a wavelength of 219 nanometers (nm). The resulting graphs show milli-absorbance units (mAU) on the Y-axis and minutes (min) on the X-axis.

The level of acetic acid in exhaust gas or smoke from burning conventional wood pellets had a chromatographic peak at 5.789 minutes or a retention time of 3.983 minutes (FIG. 1). However, the peak demonstrating the level of acetic acid in exhaust gas or smoke from burning the conventional wood pellet was absent from the exhaust gas when the wood biomass fuel pellet was burned as demonstrated in FIG. 2. Specifically, the absence of the peak at 5.789 minutes (or a retention time of 3.983 minutes) demonstrated that there was no acetic acid in the exhaust gas. Therefore, the combination of wood biomass and calcium carbonate in the wood biomass fuel resulted in a neutralized chemical reaction such that in this example, no acetic acid was present.

The present invention is not limited to a specific method for producing an advanced wood pellet that comprises calcium carbonate and a more neutral pH. One preferred embodiment of a method for producing an advanced wood pellet, wood material may be produced into a pellet using the exemplary operating system. As represented in FIG. 3, the tree (not shown) may be cut into logs 12 of desired size. The logs 12 may be transported by a conveyor belt 14 to a debarker 18. The debarker 18 may remove the bark (not shown) from the log 12. The debarker 18 may be a ring debarker, a drum debarker, or a Rosserhead debarker. Next, the log 12 may be transported by a conveyor belt 14 to a log chipper 20. The log 12 may be fragmented into chips inside the log chipper 20. The size of the chips may depend on the specification of the hammer mill for continuous material flow. The chips (not shown) may be fed into a chip bin 22, which feeds a conveyor belt 14 powered by a motor 40 controlled by a variable speed drive 42. The conveyor belt 14 transports the chips (not shown) to a screen feed bin 34 prior to entering a shaker screen 32. Inside the shaker screen 34, the chips may be separated based on their size. In some embodiments, the predetermined size may be ¼ of an inch. Chips (not shown) having a size greater than the predetermined size, may be fed to a hopper 36 connected to a screw conveyor 16. The screw conveyor 16 may be powered by a motor 40 controlled by a variable speed drive 42. The screw conveyor 16 may transport the chips (not shown) having a size greater than the predetermined size to a hammer mill 30 to further reduce the size of the chips (not shown). The output of the hammer mill 30 may be fed onto a conveyor 14 operatively connected to a bin 28 containing the chips (not shown) having the predetermined size. Chips (not shown) having a size of less than the predetermined size, may be fed to a hopper 38 connected to a screw conveyor 16. The screw conveyor 16 may be powered by a motor 40 controlled by a variable speed drive 42. The screw conveyor 16 may transport the chips (not shown) having a size of less than the predetermined size to the bin 28 containing the chips (not shown) having the predetermined size.

The bark (not shown) may be fed to a bark bin 24 which may be connected to a screw conveyor 16 powered by a motor 40 controlled by a variable speed drive 42. The bark (not shown) and the chips (not shown) present in the bin 28 may be fed into a tumble dryer 26. The tumble dryer 26 may dry the chips and bark to a moisture content between about 10% and 25%. The tumble dryer 26 may be operatively connected to a conveyor belt 14 powered by a motor 40 controlled by a variable speed drive 42. The conveyor belt 14 may feed the dried chips and bark (not shown) to a finished chips hopper 44 which may be connected to a screw conveyor 16 powered by a motor 40 controlled by a variable speed drive 42. The screw conveyor 16 may transport the dried chips (not shown) into a mixing conveyor belt 63. A predetermined amount of CaCO₃ may be fed into the mixing conveyor belt 63 by a dispenser 46. The mixing conveyor belt 63 may feed the mixture into a mixing bin 48. The mixing bin 48 may be operatively connected to a screw conveyor 16 powered by a motor 40 controlled by a variable speed drive 42. The mixture (not shown) may be fed into a pellet mill 52. No binding agents are added to the pellet mill 52. The mixture (not shown) may be then pelletized inside the pellet mill 52 forming the advanced wood pellets 10. The advanced wood pellets 10 may have a length/diameter ratio of 2:1 to optimize the combustion and emission process. The advanced wood pellets 10 may be transported by a cooling conveyer 50 into a advanced wood pelletsbin 54. Then, the advanced wood pellets 10 may be transported by a screw conveyor 16 to a storage bin 55. The advanced wood pellets may be transported to distributers and/or users. The user (not shown) may feed the advanced wood pellets 10 to a wood pellet boiler or stove 56. The boiler or stove 56 may emit heat 60 to the surrounding areas. Any ash 58 that may be a byproduct of the combustion of the wood biomass fuel pellet coming out of the stove or boiler 56 may have a low pH and may be used as filler for fertilizers and concrete. While the limited gas emission 62 produced by the stove or boiler 56 may contain water and CO₂.

FIG. 4 illustrates a block flow diagram of a system 100 for producing advanced wood pellets 10 according to the exemplary embodiment of FIG. 3.

In one embodiment, a mixture of wood biomass evenly coated with calcium carbonate may be introduced into a pellet mill. Pellet mills generally have at least one roller and at least one die, where the die may have a plurality of die holes. The roller may have a plurality of paddles such that the paddles are in contact with and create pressure against the die and the proximal end of the die holes as the roller is driven over the die at a specific pressure and rate. The wood biomass mixture may be introduced to the pellet mill in a manner that presents the wood biomass to the paddles of the roller as the roller is driven over the die. The paddles may be specifically designed such that they compress the wood biomass and drive the wood biomass into the die and the proximal end of the die holes. The compression and the heat generated under the pressure assists in the chemical reaction between the acids of the wood biomass and the calcium carbonate. For example, the pressure may generate heat ranging from a temperature of about 550° F. to about 650° F., more preferably at a temperature of about 570° F. As additional wood biomass is introduced (see, for example, FIG. 2), the inventive wood biomass fuel production repeats by again introducing another mixture of wood biomass and calcium carbonate to the roller and die and driving more of the wood biomass and calcium carbonate mixture into the die and the proximal end of the die holes. As the new supply of material is driven into the proximal end of the die holes, the previous wood biomass and calcium carbonate mixture that may be found residing in the proximal end of the die hole is then driven towards the distal end of the die holes to form a wood biomass fuel in the shape of a pellet Additionally, the heat resulting from the friction and pressure may cause a wood biomass mixture to maintain its form as a pellet as it exits the distal end of the die holes. This method of producing a clean burning wood biomass fuel is advantageous and an improvement over the art in that only two ingredients or starting materials are needed, i.e., wood biomass and calcium carbonate. Only essentially two suppliers would be necessary to provide the wood biomass and the calcium carbonate. By having fewer starting material ingredients, the machinery necessary for executing the method may also require fewer parts and elements, thereby expediting the time from loading the starting materials to the completion and production of the desired clean burning wood biomass fuel. If the demand is great enough, the wood biomass fuel may be produced at such a rate that there would be little storage time and as soon as the wood biomass fuel is packaged, it could be immediately transported to the distributor or consumer. Although the energy needed to produce the wood biomass fuel may seem to be great, the benefits of the production of the clean burning wood biomass fuel and the fuel itself may outweigh the energy input.

EXAMPLES Example 1 Neutralization of Acetic Acid in Wood Biomass

Burning 1 kg of wood may typically produce approximately 1.8 to 2.4 g of acetic acid. The chemical make-up of the acetic acid is 2CH₃COOH. However, when the acetic acid reacts with calcium carbonate at elevated temperatures, the reaction creates water (H₂O), carbon dioxide (CO₂), and calcium acetate or calcium ethanoate [Ca(C₂H₃O₂)₂]. This chemical reaction basically neutralizes or eliminates the largest occurring acid, i.e., acetic acid, in the byproducts, smoke and ash.

Example 2 Method of Producing a Clean Burning Wood Biomass Fuel Pellet

Based on a one ton batch, 18 kilograms (kg) of calcium carbonate (CaCO₃) having a particle size of about 0.2 microns was evenly distributed onto 907 kg of Northern white pine wood chips ( 3/16-inch; moisture content of about 12%) such that at least about 80% of the surface of the wood chips was covered. The mixture of CaCO₃ and wood chips was then mixed in a mixer. The mixture was then conveyed to a pellet mill (Model 26LM; Andritz Sprout A/S; Muncy, Pa., USA) which milled or compressed the mixture in a pellet die of the pellet mill at a rate of about 517 RPM under a temperature of 575° F. for about 0.5 second to form wood biomass fuel pellets. As is understood in the art, the rate of milling depends on the size and capability of the pellet mill. After the pellet has been formed, they may be immediately cooled down or through the final processing step for transport, i.e., cooled down indirectly. They may then be prepared for storage and/or transporting to their final destination. The pellets that were produced are approximately ½-inch in length and ¼-inch in diameter.

It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.

Features of the various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the disclosure can be modified, if necessary, with various configurations, and concepts of the various patents, applications, and publications to provide yet further embodiments of the disclosure.

These and other changes can be made to the disclosure in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the disclosure to the specific embodiments disclosed in the specification and the claims, but should be construed to include all systems and methods that operate in accordance with the claims. Accordingly, the invention is not limited by the disclosure, but instead its scope is to be determined broadly by the following claims. 

1. An advanced wood pellet, consisting of: calcium carbonate; and a hardwood wood material, wherein a ratio of the calcium carbonate to the wood material, ranges between 0.01 weight percent to about 0.05 weight percent.
 2. An advanced wood pellet of claim 1, that consists of a pH level between 6 and
 8. 3. (canceled)
 4. An advanced wood pellet, consisting of: calcium carbonate; and hardwood, wherein a ratio of the calcium carbonate to the hardwood, ranges between about 0.01 weight percent to about 0.05 weight percent.
 5. An advanced wood pellet of claim 4, that consists of a pH level between 6 and
 8. 6. An advanced wood pellet of claim 5, wherein the advanced wood pellet produces less ash during combustion.
 7. The advanced wood pellet of claim 4, wherein an advanced wood pellet burns 11 percent hotter during combustion when compared to traditional wood pellets.
 8. (canceled) 